When ring grooves are made perpendicular to splines, the sides of the grooves are notched by the splines; as a result, the contact area with the side faces of the locking ring is discontinuous and of a reduced area, and eventual axial forces between the shaft and the female part cause contact pressures in this area which may be excessive and damage the locking ring, especially when one of the coupled parts is made of a very hard material, as is the case, for example, in universal transmission joints in which a body forming the race or track for rolling elements constitutes a female part integral with a shaft or axle.
Damage to the side faces of the locking ring is a significant disadvantage in the case of couplings in which one of the grooves has a flank which is inclined or beveled to exert a radial thrust on the locking ring when opposed axial forces are applied respectively to the shaft and the female part, this radial thrust being sufficient, for large enough axial forces, to elastically deform the locking ring enough to extract it from the groove with the inclined flank, thus allowing axial disconnection of the shaft and the female part. The sliding of the locking ring on the notched inclined flank of the groove may be impeded, during dissassembly if its side faces are superficially slightly indented, for example, with ridges due to contact with machining marks of the sides of the groove.
The object of the present invention is to eliminate the above disadvantages by making the locking ring of a material to give it not only the elasticity required for its introduction by deformation into the groove, but also sufficient hardness to keep its side faces from being damaged by the notched sides of the groove.
The locking rings are usually made of a so-called spring steel, that is, with a reasonably high carbon content--of about 0.6 to 0.7%--, with satisfactory spring characteristics, but its insufficient hardness cannot be increased, by thermal hardening treatment followed by drawing, without reducing its toughness or resilience, that is, without increasing its brittleness.
Mild steels--with a carbon content of about 0.1%--on the other hand have good ductility allowing parts such as the locking rings to be easily formed, and maintain sufficient resilience after surface layer hardening by case hardening consisting of increasing the carbon content in a thin surface layer and then subjecting it to thermal hardening. Such hardening along the entire surface of the locking ring gives it the required elasticity, but the surface hardness (about 800 vickers) is not enough to resist high contact pressures from adjacent parts made of very hard steel. Moreover, the hardening following the case hardening is done at very high temperatures--about 850.degree. C.--requiring a large expenditure of heat energy and perhaps causing unacceptable distortion or deformation of the parts treated.